Measuring Technology of Anemometer and Its Selection
Probe Selection for Anemometers
The measurement range of flow velocity from 0 to 100m/s can be divided into three sections: low speed: 0 to 5m/s; medium speed: 5 to 40m/s; high speed: 40 to 100m/s. The thermal probe of the anemometer is used for the measurement of 0 to 5m/s; the wheel probe of the anemometer is ideal for measuring the flow velocity of 5 to 40m/s; and the best results can be obtained in the high speed range by using the pitot tube. An additional criterion for the correct selection of the flow rate probe of the anemometer is the temperature. Usually, the temperature of the thermal sensor of the anemometer is about +-70C. The rotor probe of the special anemometer can reach 350C. Pitot tubes are used above +350C.
Thermal probes for anemometers
The working principle of the thermal probe of the anemometer is based on the cold impact airflow taking away the heat on the heating element. With the help of an adjustment switch to keep the temperature constant, the adjustment current is proportional to the flow rate. When using thermal probes in turbulent flow, airflow from all directions impinges on the thermal element simultaneously, which can affect the accuracy of the measurement results. When measuring in turbulent flow, the indication value of the thermal anemometer flow sensor is often higher than that of the rotary probe. The above phenomenon can be observed in the pipeline measurement process. Depending on the design of the managed pipe turbulence, it can occur even at low speeds. Therefore, the anemometer measurement process should be carried out on the straight part of the pipeline. The starting point of the straight line should be at least 10×D (D=pipe diameter in CM) before the measurement point; the end point should be at least 4×D behind the measurement point. The flow section must not be obstructed in any way. (angles, resuspensions, objects, etc.)
Rotary Probe for Anemometers
The working principle of the rotating wheel probe of the anemometer is based on converting the rotation into an electrical signal. First, it passes through a proximity sensor, "counts" the rotation of the rotating wheel and generates a pulse series, and then converts it through the detector to obtain the rotational speed value. The large-diameter probe (60mm, 100mm) of the anemometer is suitable for measuring turbulent flow with medium and small flow rates (such as at the outlet of the pipeline). The small-caliber probe of the anemometer is more suitable for measuring the airflow where the cross-section of the pipe is more than 100 times larger than the cross-section of the probe.
